In the last few years, high-resolution video displays, e.g., high definition televisions (HDTVs) and flat panel displays (FPDs), have become commonplace in the video display market. When using these high-resolution video displays to display a video signal from a normal resolution source, e.g., digital video disk (DVD) or videocassette recorder (VCR), the normal resolution signal must be scaled to a high-resolution signal. The scaled high-resolution signal often lacks high frequency components that cause the displayed image to look soft or out of focus. While it is difficult to recover details lost to scaling, the apparent sharpness of a displayed image may be improved by image edge enhancement.
To enhance the edges of an image, the luminance, the chrominance, or both components of the video signal corresponding to the edges need to have their transitions enhanced. Many techniques for enhancing edge transitions exist. For instance, optimizing a traditional sharpening filter with a distortion component enhances the edge transitions, where the distortion component is derived from either the amplitude (luminance portion) or color frequency response (chrominance portion) of the edge to be sharpened. The luminance technique, however, is dependent upon the original amplitude of each edge, and thus causes a disproportionate number of enhancements to be applied to low amplitude details. And using a distortion component may generate false edges and image ringing when the input video signal is outside of the traditional sharpening filter's predetermined amplitude or frequency range. The chrominance implementation also generates false edges and image ringing when there are several closely spaced high frequency details. Furthermore, the chrominance implementation may only be performed in those areas enhanced by the luminance technique.
To limit this problem of generating false images and image ringing, one approach only displays edge enhancements in areas defined by prior images of the video signal. Thus, false images and image ringing due to edge enhancements, as well as the edge enhancements themselves, only occur in those defined areas. The limitation of false images and image ringing, therefore, comes at an overall image sharpness loss.
Accordingly, a need remains for an improved image edge enhancement system and method that enhances image edges regardless of the input video signal source or content without creating false images or generating image ringing.